1. Field of the Invention
The invention relates to a polyester imide resin insulating coating material used for an insulating coating of magnet wire, etc., and in particular, to a polyester imide resin insulating coating material by which a polyester imide resin based insulating film having improved partial discharge resistant characteristics is obtained, and an insulated wire having an insulated film formed of the coating material.
2. Description of the Related Art
As an insulated wire used for a coil of electric equipment such as motor or transformer, an insulated wire having an insulating film formed of a polyester imide resin insulating coating material formed by adding an alcohol component as a crosslinking component to an imide dicarboxylic acid which is obtained by synthesizing a diamine component and an acid component such as tricarboxylic acid anhydride so as to be an excessive acid state is generally used for an application requiring heat resistance greater than that of Class F. In addition, an insulated wire in which a polyamide imide resin-based insulating film, an insulating film having self-lubricating properties or an insulating film having self-bonding properties is formed on the insulating film formed of the polyester imide resin insulating coating material as described above is also used. The polyester imide resin insulating coating material and the insulated wire having an insulating film formed thereof are widely used since high heat resistance is obtained with relatively low cost.
Specifically, as the most versatile polyester imide resin insulating coating material at the moment, there is a THEIC modified polyester imide which is formed by adding an alcohol component formed of tris(2-hydroxyethyl)isocyanurate (THEIC) to an imide dicarboxylic acid. The polyester imide resin insulating coating material can improve heat resistance and refrigerant resistance since glycerin or THEIC, etc., which is a trifunctional alcohol component is introduced therein as a crosslinking component.
On the other hand, a motor, etc., is recently often driven by inverter in order to improve efficiency of a coil of electric equipment such as a motor. There are many cases that partial discharge occurs between adjacent insulated wires due to generation of excessive voltage (inverter surge voltage) in a coil during such inverter drive and causes deterioration of an insulating film, leading to breakdown.
As a method of reducing the deterioration of an insulation film caused by partial discharge, for example, JP-A 2009-277369 proposes an insulated wire composed of a conductor and an insulating film for coating the conductor and having an insulating layer formed by applying and baking a mixed resin of polyester imide and polyether sulfone. According to JP-A 2009-277369, an insulated wire with high corona inception voltage (partial discharge inception voltage) (the peak value of about 940V and the effective value of about 670V) as well as excellent in mechanical strength such as hardness or in heat resistance is obtained by providing the insulation layer formed by applying and baking a resin composition including a mixed resin of polyester imide and polyether sulfone.